The invention relates to an information storage system comprising a device and a record carrier. The device comprises a radiation source for generating a radiation beam for scanning the record carrier, and a pulse generator for generating write pulses erase pulses. The generator has an output connected to an input of a modulator for modulating the intensity of the radiation beam. The modulator may be a separate optical element arranged so that it is in the radiation path of the radiation beam, or it may be integrated with the radiation source if it is a radiation source which can be modulated and directly supplies an intensity-modulated radiation beam. The record carrier has a recording layer in which information can be (a) written by changing an area of the recording layer having an amorphous structure by means of write pulses of the radiation beam into an information area having a crystalline structure and (b) erased by heating an information area above the melting point of the recording layer by means of erase pulses of the radiation beam. The invention also relates to the device and the record carrier used in such a system.
A system of the type described in the opening paragraph is known from an article entitled "Optical memory" by P. Chaudhari and C. B. Zarowin in the IBM Technical Disclosure Bulletin, vol. 16, no. 2, July 1973, pp. 568 and 569. In that system, a crystalline information area in an initially amorphous material is written by means of a pulsed and focused radiation beam. The information area is erased by rendering the material amorphous again by means of an erase pulse at the information area. The erase pulse has a shorter pulse duration and a larger amplitude than the write pulse. However, it has been found that upon reading information which has been written after erasure, a read signal is obtained which is not optimum and has a signal-to-noise ratio which is too low.